Powder coating composition comprising epoxy group-containing acrylic resin

Abstract

An epoxy group-containing acrylic resin for a powder coating composition is a copolymer, having a weight-average molecular weight of 3000 to 20000, of a vinyl monomer mixture comprising 10 to 60% by weight of alkyl ester(s) of (meth)acrylic acid, 10 to 60% by weight of epoxy group-containing vinyl monomer(s) and other vinyl monomer(s), said epoxy group-containing acrylic resin having a mean particle diameter in the range of 80 to 800 mum, including 95% by weight or more of particles satisfying the relation of 1<=R/r<=1.2 wherein R is a long diameter and r is a short diameter of each particle, and including 1000 ppm or less of volatile components, the amount of the particles having long diameters R of less than 62 mum being 5% by weight or less, that of the particles having short diameters r of more than 1000 mum being 5% by weight or less.

What is claimed is:  
     
       1. A powder coating composition comprising an epoxy group-containing acrylic resin particles and a curing agent, said curing agent contained to cure the epoxy group-containing acrylic resin particles and form a coating on a substrate, said epoxy group-containing acrylic resin particles 
       (i) being a copolymer, having a weight-average molecular weight of 3000 to 20000, of a vinyl monomer mixture comprising 10 to 60% by weight of alkyl ester(s) of (meth)acrylic acid, 10 to 60% by weight of epoxy group-containing vinyl monomer(s) and other vinyl monomer(s),  
       (ii) having a mean particle diameter in the range of 80 to 800 μm,  
       (iii) including 95% by weight or more of particles satisfying the relation of 1≦R/r≦1.2 wherein R is a long diameter and r is a short diameter of each particle,  
       (iv) comprising 5% by weight or less of particles having long diameters R of less than 62 μm and 5% by weight or less of particles having short diameters r of more than 1000 μm,  
       (v) including 1000 ppm or less of volatile components, and  
       (vi) having an epoxy equivalent in the range of 350 to 1200 g/eq.  
     
     
       2. The powder coating composition according to  claim 1  wherein the other vinyl monomer(s) is styrene monomer(s) and is contained in an amount of 10 to 50% by weight in the vinyl monomer mixture. 
     
     
       3. The powder coating composition according to  claim 1  wherein said epoxy group-containing acrylic resin is prepared by a suspension polymerization method. 
     
     
       4. The powder coating composition according to  claim 1  wherein said epoxy group-containing acrylic resin is prepared by the suspension polymerization method in which terpinolene is used as a chain transfer agent. 
     
     
       5. The powder coating composition according to  claim 1 , which is prepared by polymerizing a monomer mixture comprising 10 to 60% by weight of alkyl ester(s) of (meth)acrylic acid, 10 to 60% by weight of epoxy group-containing vinyl monomer(s), and other vinyl monomer(s) by suspension polymerization at a polymerization temperature of 80° C. or higher under a polymerization pressure of 2 kg/cm 2  or higher, followed by removing volatile components included in the suspension polymer.